[PATCH 07/21] drm/amdkfd: Clean up KFD_MMAP_ offset handling

[Felix Kuehling]

On 2018-05-11 04:52 AM, Oded Gabbay wrote:
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
>> @@ -41,9 +41,33 @@
>>
>>  #define KFD_SYSFS_FILE_MODE 0444
>>
>> -#define KFD_MMAP_DOORBELL_MASK 0x8000000000000ull
>> -#define KFD_MMAP_EVENTS_MASK 0x4000000000000ull
>> -#define KFD_MMAP_RESERVED_MEM_MASK 0x2000000000000ull
>> +/* GPU ID hash width in bits */
>> +#define KFD_GPU_ID_HASH_WIDTH 16
>> +
>> +/* Use upper bits of mmap offset to store KFD driver specific information.
>> + * BITS[63:62] - Encode MMAP type
>> + * BITS[61:46] - Encode gpu_id. To identify to which GPU the offset belongs to
>> + * BITS[45:0]  - MMAP offset value
>> + *
>> + * NOTE: struct vm_area_struct.vm_pgoff uses offset in pages. Hence, these
>> + *  defines are w.r.t to PAGE_SIZE
>> + */
>> +#define KFD_MMAP_TYPE_SHIFT    (62 - PAGE_SHIFT)
>> +#define KFD_MMAP_TYPE_MASK     (0x3ULL << KFD_MMAP_TYPE_SHIFT)
>> +#define KFD_MMAP_TYPE_DOORBELL (0x3ULL << KFD_MMAP_TYPE_SHIFT)
>> +#define KFD_MMAP_TYPE_EVENTS   (0x2ULL << KFD_MMAP_TYPE_SHIFT)
>> +#define KFD_MMAP_TYPE_RESERVED_MEM     (0x1ULL << KFD_MMAP_TYPE_SHIFT)
> Isn't this new definition breaks existing user-space library (kfd thunk) ?
> If that is the case we have a problem here.

No, this does not break user mode, because user mode isn't aware of
these definitions at all. The mmap offset comes from kernel mode and is
opaque to user mode. User mode just passes it back down to kernel mode
in the offset parameter of mmap. So the kernel can change the encoding
of the mmap offset without breaking user mode.

Regards,
  Felix

>
> Oded
>
>